Carbon nanotubes (CNT) have been the subject of intense research since their discovery in 1991. CNT's possess unique properties such as small size and electrical conductivity, which makes them suitable in a wide range of applications, including use as structural materials in molecular electronics, nanoelectronic components, and field emission displays. Carbon nanotubes may be either multi-walled (MWNTs) or single-walled (SWNTs), and have diameters in the nanometer range.
Depending on their atomic structure CNT's may have either metallic or semiconductor properties, and these properties, in combination with their small dimensions makes them particularly attractive for use in fabrication of nano-devices. A major obstacle to such efforts has been the diversity of tube diameters, chiral angles, and aggregation states in nanotube samples obtained from the various preparation methods. Aggregation is particularly problematic because the highly polarizable, smooth-sided fullerene tubes readily form parallel bundles or ropes with a large van der Waals binding energy. This bundling perturbs the electronic structure of the tubes, and it confounds all attempts to separate the tubes by size or type or to use them as individual macromolecular species.
There have been many reports on producing suspensions enriched in individual fullerene tubes (J. Liu et al., Science 280, 1253 (1998); M. J. O'Connell et al., Chem. Phys. Lett. 342, 265 (2001); S. Bandow et al., J. Phys. Chem. B 101, 8839 (1997); J. Chen et al., Science 282, 95 (1998); G. S. Duesberg, J. Muster, V. Krstic, M. Burghard, S. Roth, Appl. Phys. A 67, 117 (1998); A. B. Dalton et al., J. Phys. Chem. B 104, 10012 (2000); A. B. Dalton et al., Synth. Metals 121, 1217 (2001); R. Bandyopadhyaya, E. Nativ-Roth, O. Regev, R. Yerushalmi-Rozen, Nano Lett. 2, 25 (2002)), available samples have still been dominated by small nanotube bundles. M. O'Connell et al (Science 297, 593 (2002)) has described a method based on vigorous treatment with a sonicator followed by centrifugation, primarily yielding individual fullerene nanotubes in aqueous micellar suspensions. Also described are processes (M. O'Connell et al., Chem. Phys. Lett., 342, 265, 2001; WO 02/076888) for the solubilization of carbon nanotubes in water by association with selected polymers, although not all polymers tried were successful.
Once the nanotubes are in a dispersed form suitable for further manipulation, a desirable next step is self-assembly of the nanotubes on a solid substrate. Associating oligonucleotides to carbon nanotubes would allow one to use bimolecular techniques for the positioning of the nanotubes on a substrate. K. A. Williams et al (AIP Conf. Proc. 663, 444, 2002) has covalently coupled peptide nucleic acid oligomers to carbon nanotubes and then hybridized this construct to DNA. However, DNA was not directly attached to the nanotubes, nor was dispersion of nanotube bundles observed.
The problem to be solved, therefore, is to provide a method for the facile and inexpensive solubilization and dispersion of bundled carbon nanotubes for use in the fabrication of nano-devices. Applicants have solved the stated problem through the discovery that stabilized solutions of nucleic acid molecules have the ability to disperse and solubilize carbon nanotubes, resulting in the formation of nanotube-nucleic acid complexes. Although complexes of nucleic acids and carbon nanotubes are known, the present complexes are new, in that the association between the nanotube and nucleic acid is non-covalent and not through the interaction of specific functionalized groups.